The present invention relates to a rechargeable battery having at least two series-connected cells which are located one above the other in a stack and have flat electrodes, wherein the ends of the stack form the poles of the rechargeable battery, and the electrodes have connecting lines which emerge from the stack at the side.
Recently, rechargeable batteries such as these have also been used in electrical drive systems for motor vehicles, in order to form high rechargeable-battery pole voltages of more than 100 V by stacking and series connection of an appropriately large number of flat cells.
However, the series connection of the cells has the disadvantage that all the cells are charged with the same charging current, and therefore even minor quality differences between the individual cells lead to different states of charge. Numerous circuits for charge balancing between the individual cells have therefore already been proposed, which access the individual electrodes of the cells and are either based on individual-cell charge destruction via a resistance network, cell recharging via capacitors, or inductive energy transmission between the cells. The latter variant is referred to as inductive charge balancing and is described, for example, in the documents DE 195 33 543 A1 and DE 44 22 409 A1.
In the case of inductive charge balancing, the individual cells are connected alternately via switches to coils, which are inductively coupled via a common core. The energy which is emitted from a cell with a relatively high state of charge is converted in the build-up of a magnetic field, whose dissipation is converted back to charge energy for a cell with a lower state of charge when the switch is switched over, thus resulting in a charge equalization between all the cells as the switching process progresses. Inductive charge balancing has the major advantage that it automatically results in galvanic isolation of the cells. However, one disadvantage is the high level of wiring complexity for the connection of the individual cells to the coils which are used for energy charge changing. In the case of rechargeable batteries which are formed from a large number of cells, for example tens or hundreds of cells, the high level of wiring complexity is at the moment prohibitive for practical use of inductive charge balancing.
The aim of the invention is to overcome the described disadvantages of the prior art and to provide a rechargeable battery composed of stacked cells which allows operation with inductive charge balancing in a simple and cost-effective manner.